Communications that use satellites provide advantages not available to solely ground-based communications, but might also be subject to more constraints than ground-based communications. For example, satellites must remain in orbit a certain distance above the surface of the Earth, one satellite cannot cover the Earth's entire surface at one time, and other than geosynchronous satellites, the satellites move relative to the Earth's surface. As a result, it is often required to use a constellation of satellites and, where one ground-based user device needs to communicate with another one ground-based user device but they are not both within a footprint of one satellite, inter-satellite communications might be required. A geostationary satellite might have a footprint that is large enough so that the Earth's entire surface can be covered by four satellite footprints, but with low Earth orbit (LEO) satellites, the footprints might be approximately circular with diameters of around 1,000 km. In that case, it might require a constellation of around 1,000 to 2,000 satellites in order to have footprints that cover the Earth's entire surface in distinct orbital planes continuously. Even with geostationary satellites, which orbit approximately in a plane that includes the Earth's equator, full coverage is not simple, as the poles are not well covered by geostationary satellites and constellations using distinct orbital planes might be needed, such as a constellation of geostationary satellites and polar satellites.
If the source device and the destination device are both within one satellite's footprint, the source device can send data to the satellite by transmitting a signal that is received by the satellite and the satellite can send the data to the destination device by transmitting a signal that is received by the destination device. More is needed if the source device and destination device are not both within a footprint of one satellite. In that case, the data has to get from one footprint to another footprint. More specifically, the link path from the source device to the destination device is more than just the path from the source device to the satellite to the destination device.
In some approaches, a constellation comprises a plurality of orbital planes and routing of data communications satellite is done on a grid-like basis, where data is transmitted from one satellite to another one that is forward of the transmitter (referred to as north, even though it might not be the same direction as North on the Earth's surface below the transmitter), one that is aft (south) of the transmitter, to one side (west) or the other (east) of the transmitter. While the aft and forward receivers might be in a stable orientation relative to the transmitter, the east and west satellites are in different orbital planes, so their orientation relative to the transmitter varies. This might require wideband antennas that can be inefficient, costly and add to link budgets, weight budgets, and power budgets.
Satellite communications systems are often needed to provide global, or near-global, coverage of the planet such that individuals and businesses can remain connected and receive/send information (i.e., phone calls, messages, data, etc.) at any time in near real-time or otherwise.
Improved inter-satellite link communications might overcome some of the limitations described above.